Gravure printing for flexible packaging materials, flexographic printing for sanitary materials, silk screen printing for metal plates, inkjet printing for indoor and outdoor advertisement, and the like, have been generally known as printing methods suitable for non-absorbable printing media. However, ink compositions used for these printing methods generally comprise solvents such as toluene, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone. In this case, obligations such as an ambient concentration setting, the installation of a local exhauster because of smells or the like, and regular medical examinations, are imposed. Thus, handling is difficult. Therefore, inks having higher safety and health properties are required. In particular, unlike gravure printing, flexographic printing and silk screen printing which are performed in exclusive factories, inkjet printing is used in ordinary business offices so that it is required to give more consideration to safety, hazardousness and odour.
With regard to gravure printing for flexible packaging materials and flexographic printing for sanitary materials, non-toluene inks which do not comprise toluene whose ambient concentration set value is small or water-based inks which comprise alcohols as a main component, have been developed to improve safety.
On the other hand, in regard to inkjet printing, an ink which uses a polyalkylene glycol solvent or a hydrocarbon solvent (Japanese Patent No. 3590486) has been developed. However, such inks cannot dissolve the surface of the printing media, and thus result in poor fixity and water resistance.
In recent years, accordingly, solvent-containing inks with improved fixity and water resistance have been developed, by jointly using a nitrogen-containing heterocyclic compound such as 2-pyrrolidone or N-methyl-2-pyrrolidone or a lactone compound (JP-A-2005-60716, JP-A-2005-15672, JP-A-2005-200469, Japanese Patent No. 3692365, JP-A-2005-248006) as an assistant solvent. However, due to their strong solubility, in some cases, these materials and the odour need consideration.